brians200 50 Posted May 6, 2014 Hello, I am trying to find all the roads inside of rotated ellipse. The ellipse comes from a map marker that is created by the user. I have tried implementing the answer from here to determine if a point is in an ellipse. _u = cos(_angle) * (_ellipseX - _pointX) + sin(_angle) * (_ellipseY - _pointY); _v = -sin(_angle) * (_ellipseX - _pointX) + cos(_angle) * (_ellipseY - _pointY); _dSqr = (_u/_sizeA)*(_u/_sizeA) + (_v/_sizeB)*(_v/_sizeB); _dSqr <= 1; However, when I try this, it only works when the angle is 0, 90, 180, or 270. Any other angle produces what I can only describe as a scissor effect. Here is a series of pictures from 0 to 90 degrees, increasing the angle by 15 degrees. The green dots are the roads that the code is returning as "in the ellipse". 0 Degrees 15 Degrees 30 Degrees 45 Degrees 60 Degrees 75 Degrees 90 Degrees I also tried implementing the answer from here, and got the same results _left = (cos(_angle)*(_pointX - _ellipseX) + sin(_angle) * (_pointY - _ellipseY))/_sizeA; _right = (sin(_angle)*(_pointX - _ellipseX) - cos(_angle) * (_pointY - _ellipseY))/_sizeB; _left*_left + _right*_right <= 1; Does anybody know what is wrong with the math? The angle and ellipse size are taken from the marker using markerDir and getMarkerSize Share this post Link to post Share on other sites

Väinämöinen 0 Posted May 6, 2014 Hi, it seems that your ellipse is mirrored. What happens if you put negative value to the angle? Eg. _angle = _angle * (-1) regards.VÃ¤inÃ¤mÃ¶inen Share this post Link to post Share on other sites

brians200 50 Posted May 6, 2014 That fixes the problem! I guess it is because as you increase your angle when using North/South/East/West, you rotate clockwise. However, when working with a unit circle, you rotate counter clockwise. Thanks for your help, VÃ¤inÃ¤mÃ¶inen. Share this post Link to post Share on other sites